Single-walled carbon nanotubes (SWNTs) unavoidably exist as a mixture of metallic and semiconductive single-walled carbon nanotubes (m-SWNTs, s-SWNTs) while being synthesized. To date, no method is proposed that enables m-SWNTs or s-SWNTs to be directly obtained in pure form during the synthesis process.
Accordingly, there is a need for a method that can be used to selectively obtain carbon nanotubes of specific properties based on m-SWNTs or s-SWNTs, using a synthesized mixture of m-SWNTs and s-SWNTs.
There are reports that functionalization of carbon nanotubes improves the properties of the carbon nanotubes, including improving dispersibility and increasing electrical resistance. It is known that functionalization on the side wall greatly changes the dispersibility and electronic properties of the carbon nanotubes.
Specifically, for example, for the purpose of minimizing the adverse effects on the conjugate system caused by the addition to the side wall, there have been attempts to introduce dendrimers with multifunctional groups to the side walls of carbon nanotubes. Further, it is also known that introducing organosilicon groups to the side walls improves the field emission characteristics of the carbon nanotubes, or develops n-type field-effect transistor (FET) characteristics. Indeed, the functionalization of the carbon nanotubes by functionalization is important for controlling the properties of the carbon nanotubes.
However, there are only a few reports concerning a technique that chemically modifies m-SWNTs or s-SWNTs through selective chemical reaction with a reagent. It is expected that the chemical reaction based on the electrical properties of carbon nanotubes would be useful for the separation of carbon nanotubes of different electrical properties, or for improving properties as a FET material.
Patent Document and Non-Patent Documents 1 and 2 describe chemically reacting carbon nanotubes with cyclic disulfides under ultraviolet irradiation. However, these publications are not suggestive of a finding with regard to the reactivity of the carbon nanotubes and linear disulfides, or selective functionalization based on the electrical properties or diameter of the carbon nanotubes.    Patent Document 1: JP-A-2006-131428    Non-Patent Document 1: Chemistry Letters 2006, 35, 742.    Non-Patent Document 2: Diamond & Related Materials 2007, 16, 1091-1094.